This invention relates to the field of electrical conduit installation and, more particularly, to apparatus and methods for bending electrical conduit.
In many conduit applications, local building codes require that wires, particularly electrical wires, be enclosed in pipes or conduit, primarily for safety reasons. Various types of conduit are used for this purpose including EMT (Electrical Metallic Tubing), also called "thinwall"; IMC (Intermediate Metallic Conduit), a thicker material assembled with threaded couplers; and "Rigid," the heaviest conduit generally used in electrical work. All of these conduits are made of a metal such as aluminum or steel.
Conduit is sold commercially in straight pieces of various lengths. In the course of installing conduit in or along a wall, it is necessary to bend the conduit to avoid doorways, ducting and other obstructions. An electrician can bend small-diameter, thinwall conduit by hand. Bending heavier conduit requires a bending machine. Various bending machines are known, including mechanical, hydraulic and electric models. Mechanical bending machines are used most frequently because they are adequate for bending pipe up to 11/2 to 2 inches OD and they are less expensive than powered machines.
A common conduit bending task is to form an "offset", i.e., a pair of equal and opposite bends in a length of conduit such that the end portions of the conduit are parallel to, but offset from, each other. For example, where a conduit is to be installed horizontally in a wall, but a vent obstructs its path,
an offset would be formed in the conduit so that, when installed, it passes by--either above or below--the obstruction, and resumes a horizontal orientation.
Another conduit bending task is to form a "saddle". A saddle consists of a first offset and a complementary offset, equal and opposite to the first offset. The saddle thus includes four bends, arranged such that a U-shaped detour is formed in the conduit to circumvent an obstruction.
It is critical that offsets and saddles be formed such that the entire length of the bent conduit lies in a plane so that, upon installation, the conduit fits inside or flush against the wall. If any bend after the first bend is made improperly, a section of the conduit will extend outside the plane. Such an errant section of pipe is known as a "wow" or "dogleg".
Conduit bending may be done on elaborate and expensive "bending tables". Simpler bending machines also may be used, but all bending machines require "leveling" the conduit in the bending machine to form an offset or a saddle. "Leveling" means rotationally positioning the pipe relative to a reference plane, for example a horizontal plane, prior to forming each bend.
One method of leveling a conduit is sometimes called "Eyeballing". As the name implies, the operator simply uses his naked eyesight to view the bend after it is made to determine if a level position has been achieved. The method requires the operator to "eyeball" the bend from various angles and therefore is time consuming. Accuracy depends solely upon the skill of the operator and can be extremely poor if the operator's skills are low. Material loss and labor expense using this method can be very high.
Another known leveling method requires assembling a pair of locking pliers (for example, Vise-Grips), a length of square channel ("Kindorf") stock, and a magnetic torpedo-type level. The operator applies the locking pliers to attach the channel stock to an open end of the conduit pipe to be bent. The magnetic torpedo level is then (magnetically) attached to the channel stock. The operator views the torpedo level to aid him or her in leveling the conduit relative to a horizontal plane.
The foregoing method is time consuming and unreliable. The orientation of the three detachable parts is critical, so that if any of them is bumped while bending the conduit, a dogleg is likely to result. The locking pliers are not a stable attachment means because the plier jaws do not fittingly engage the inside contour of the pipe to be bent. An inaccurate bend can result if the pliers shift during the bending process.
Another problem with this makeshift level is that the bubble level indicator in the torpedo level is not clearly visible from the position from which the operator makes the bends. The operator must move around the bending machine and the pipe being bent to adjust for level. These added footsteps increase the time required for bending.
A variation on the torpedo level theme requires fashioning a special tool by welding a metal plate perpendicular to the stable arm of a pair of locking pliers. The modified pliers are clamped onto the end of the conduit pipe to be bent, and a magnetic torpedo level is positioned on the metal plate. This makeshift leveling device is used in a manner similar to the three-part device described above. Like the three-part apparatus, the welded-plate pliers do not fit the inside contour of the pipe to be bent, thus leading to an unstable attachment. Second, this level is bulky and heavy and therefore difficult to use. Finally, as with the Kindorf channel (three-piece) device, the bubble which the operator uses to judge level is not clearly visible from the position from which the operator makes the bends, again slowing the electrician's work.
Another level known for use in conduit bending is one available from the Off-Set Level Company of Ventura, California, hereinafter referred to as the "OLC device". The OLC device is similar to FIG. 2 of the drawing. The OLC device suffers shortcomings similar to the other apparatus described above in that the bubble level indicator in the OLC device is not clearly visible to the operator during all phases of a bending operation. Accordingly, it too requires the operator frequently to move about in order to check for level positioning of the conduit preparatory to bending. Additionally, the OLC device's bubble level indicator is exposed and therefore subject to being damaged or knocked out of alignment if bumped. The result is increased tool expense, unreliable results and lost time. Finally, the means for attaching the OLC device to the conduit does not fit the interior contour of the pipe, thus making it unstable and causing inaccurate results.